Solution:
A uniform magnetic field exists in the plane of the paper, pointing from left to right, as shown in the figure. In the field, an electron and a proton move, as shown. The electron and proton experience forces both pointing into the plane of the paper.We know that the direction of motion of an electron is always opposite to the direction of current flow. Here, both the proton and the electron are moving in opposite directions to each other and perpendicular to the magnetic field. Therefore, the current for both the electron and proton will move in the direction of motion of the proton. So, by Fleming’s left-hand rule, the forces for both of them will point into the plane of the paper.
